1. Field of the Invention
The present invention relates to an image failure detection unit in redundant duplex transmission and, more particularly, to an image failure detection unit in redundant duplex transmission in which a failure occurring in a regular link can be automatically detected in an instant so that the regular link can be switched to a backup link without causing any failure in an output image in the redundant duplex transmission in which the same image is transmitted via two links.
2. Description of the Related Art
There has been conventionally used a system in which the same image is transmitted via two links, and then, a normal link is selected on an output side so as to secure high reliability of image transmission. One example of such a system is illustrated in FIG. 8.
In FIG. 8, an encoder 51, a transmission line and a decoder 53 constitute a first link; and another encoder 55, another transmission line and another decoder 57 constitute a second link. A failure detection unit 54 detects a failure which may occur on the first link; and another failure detection unit 58 detects a failure which may occur on the second link. A switcher 59 selectively connects the first or second link to an output line.
The failure detection unit 54 or 58 detects a failure based on the fact that a synchronizing signal is lost from a video signal to be transmitted or the fact that a transmission error rate exceeds a predetermined value. If such a failure continues for a predetermined period of time, the failure detection unit 54 or 58 judges that a failure occurs on the transmission link, so as to start an alarm, not shown. Thereafter, the switcher 59 is manually or automatically switched to the second link in accordance with the alarm, and consequently, the second link is connected to the output line.
However, in the above-described prior art, it has taken several seconds or longer until the failure detection unit 54 or 58 detects the transmission failure to switch the switcher 59 to the other transmission link. Therefore, there has arisen a problem that the video picture with the failure is unavoidably output for the several seconds or longer.
An object of the present invention is to provide an image failure detection unit in redundant duplex transmission, in which if a failure occurs on a regular link, the failure can be detected in real time so that the regular link is instantaneously switched to a normal backup link, thus preventing outputting of an image with the failure or reducing outputting of an image with the failure.
In order to achieve the above-described object, the present invention provides an image failure detection unit in redundant duplex transmission, in which the same image is transmitted via a plurality of links and the image transmitted via a normal link is selectively used as an output image, the image failure detection unit comprising: means for determining image features per small region inside each of the images transmitted via the plurality of links; and means for comparing differences, between the links, in image feature per small region inside each of the images determined by the determining means; wherein when there is no difference in image feature per small region between the links, it is judged that the link is normal; to the contrary, when there is a difference, it is judged that a failure occurs on either of the links.
Furthermore, the present invention provides an image failure detection unit in redundant duplex transmission further comprising: means for storing the small region as a normal region in the case where there is no difference, between the links, in image feature per small region inside each of the images, while for storing the small region as a corrupted region in the case where there is a difference; and means for determining a difference in image feature between the normal region and the corrupted region; wherein it is judged that a failure occurs on the link having a greater difference.
Moreover, the present invention provides an image failure detection unit in redundant duplex transmission further comprising: means for judging whether or not the difference in image feature between the normal region and the corrupted region is a predetermined value or greater, so as to regard the failure to be significant if the difference is the predetermined value or greater; to the contrary, so as to regard the failure to be insignificant if the difference is smaller than the predetermined value; and means for deciding the disrupted link based on the majority decision of the failure judged to be significant.
According to the present invention, since the occurrence of the failure on the link can be detected by the use of the image transmitted via the plurality of links, the failure on the link can be detected in real time. Furthermore, according to the present invention, the image feature difference between the normal region and the corrupted region is determined, and consequently, it is judged that the failure occurs on the link having the greater difference, thus enhancing the accuracy of the judgment as to which link the failure occurs on. Moreover, according to the present invention, since the link on which the failure occurs is determined based on the majority of the failure judgment based on the significant difference, it is possible to further improve the accuracy of the judgment of the link on which the failure occurs and stably switch the link, thus enhancing the reliability of the detection unit.